Method for cooling ingots in continuous casting



Jan. 14, 1947. E. A. NICHOLLS 1 METHOD FOR COM-116G INGOTS IN CONTINUOUSCASTING Filed Aug. 1, 1942 2 Sheets-Sheet 1 Jan. 14, 1947. E. A.N[CHOLL$ 2,414,269

METHOD FOR COOLING INGOTS IN CONTINUOUS CASTING Filed Aug. 1, 1942 2Sheets-Sheet 2 ZDWl/V Au-wzp Mamas INVENTOR.

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ATTORNEY Patented Jan. 14, 1947 METHOD FOR COOLING moors IN CONTINUOUSoas'rmc Edwin Alfred Nicholls, Alcoa, Tenn., assignor to AluminumCompany of America, Pittsburgh, Pa., a corporation of PennsylvaniaApplication August 1, 1942, Serial No. 453,146

Claims. 1

This invention relates to the. casting of ingots by a continuous castingprocess and it is especially concerned with chilling the mold and theingot emerging therefrom.

In the continuous casting process molten metal is continuously fed intoa suitable open mold shell where it at least partially solidifies andthe solid metal body so formed is continuously withdrawn from the moldat approximately the rate at which solidification progresses upwardly.In this manner the solidified metal serves as a bottom to the open moldand holds the pool of molten metal within the mold shell once thecasting operation has begun. The rate at which molten metal isintroduced into the mold and the rate of withdrawal of the solid metalbody are obviously deof water is required and there may be a nonpendentupon the rate at which heat is extracted from the mold and the metaltherein. Both the surface condition and internal structure of thesolidified metal body are considerably affected by the rate at whichheat is extracted. Too drastic a chill may cause a rupture in the metalbody due to contraction. An insuflicient chill may permit bleeding ofthe molten metal to the outside of the freezing metal body. Anon-uniform chilling causes an undesirable variation in grain size anddistribution of undissolved constituents in the ingot. In casting ingotsof light metals, for example, aluminum and magnesium and the alloyswherein these metals predominate, the chilling must be very carefullycontrolled to maintain the proper rate of heat extraction and thus avoidthe foregoing troubles. This requirement is particularly acute whererelatively thin walled mold shells are employed, such as those which maybe about one-fourth of an inch in thickness, and any changes in chillingconditions are quickly transmitted to the freezing metal within the moldshell.

Methods of chilling molds used heretofore in the continuous castingprocess have consisted of providing water jacketed molds or directinghigh pressure sprays of water against the mold shell. The ingots havebeen cooled either by passing them through tanks of water or allowingwater from the mold to run down over the ingot surface. Water jacketedmolds are expensive to make and sometimes introduce difficulty inoperation because of possible stoppage of the water passages or theaccumulation of scale within the passage which interferes with thetransmission of heat through the mold wall. Where high pressure sprayshave been employed, such as is generally the case when the water comesdirectly from the main supply line, a considerable volume uniformchilling eifect at the point of impingement of the individual water jetsupon the mold and ingot surfaces. Another difiiculty which has beenencountered where high pressure sprays are used is that any markedfluctuation in pressure effects the chilling effect, and unless the moldoperator maintains a carefulcontrol, the flow of water is uneven, withthe result that the freezing of the metal within the mold is notuniform. This variation in chilling conditions may lead to one or moresuch defects as surface cracking of the ingot, a rupture within theingot not visible at the surface, or even a visible splitting of theingot. By surface cracking is meant cracks which extend but a shortdistance into an ingot, generally only a fraction of an inch. Thesplitting may not occur at the very beginning of the casting operationbut may happen after a considerable portion of metal has been cast. Inany event when such splitting occurs, the ingot must be subsequentlyscrapped and remelted with a consequent loss in time and expense. Anuneven flow of water also tends to produce a rough ingot surface knownas hot streaking which may introduce diiiiculties in fabricatingoperations. In casting light metal ingots of relatively large crosssectional area, especially those having a considerable thickness, one ormore of the foregoing adverse eiiects sometime occur in spite of theoperators efforts to control the chilling properly.

It is an object of my invention to provide a method of uniformlychilling mold shells and ingots in the continuous casting process.Another object is to provide a method for minimizin rough surfaces oningots made by this process which may lead to diificulty in fabricationof the ingots to finished products. Still another object is to provide amethod for minimizing the surface cracking and splitting tendenciesandimproving the uniformity of internal structure of ingots made by thecontinuous casting process. A further object is to produce uniformchilling conditions where ingots of relatively large cross sectionalarea are made. Still another object is to provide apparatus for carryingout my method, including a novel form of water distributing means bywhich the novel steps of the method are performed. These and otherobjects will become apparent in the following description of theinvention.

Generally, my invention consists of chilling the More specifically ithas been found that ingots are produced having a more uniform internalstructure, i. e. greater uniformity of grain size and jdistribution ofundissolved constituents, a smoother surface and fewer surface cracksand splits when a low pressure water spray is employed than where a highpressure spray is used. These advantages are especially evident inmaking ingots of relatively large cross sectional area, for example,those having an area of over 200 square inches. In referring to arelatively low water pressure, I mean that the pressure of the water atthe spray hole is of the order of from a few ounces to a few pounds persquare inch, for example, from about 0.5 to 3 or 4 pounds per squareinch as compared to a normal line pressure of 40 or 50 pounds per squareinch or more. The improvement is accomplished by using a low pressurecoolant system that includes a spray chamber as one of the principalparts thereof, said chamber surrounding a substantial portion of themold but separated therefrom by an air space. The space between the saidchamber and mold is preferably from 0.5 to 1 inch. The chamber surroundsthat portion of the mold where the ingot is formed and it also,preferably, extends below the bottom edge of the mold shell to providefor a spray on the emerging ingot. The chamber is provided with suitablyarranged spray holes whereby at least the external surface of the mold,and preferably the emerging ingot also, are flooded with water from thelow pressure sprays. The spray chamber may be referred to as a unitarychamber since all of the coolant for chilling the mold and ingot comesfrom one chamber instead of from two or more pipes or other conduitswhereby individual portions of the spray can be independentlycontrolled.

The use of a single unitary spray chamber surrounding a substantialportion of the mold has particular advantages in that only one watercontrol valve is required to admit water to the chamber, This obviatesthe necessity for adjustment of several valves, and promotes a uniformflow of water from the chamber, and ec-nsequently, a greater uniformityin the chilling of the mold and the hot metal therein. The use of asingle water control means also simplifies the operation where a lowpressure water supply system is employed in that the control means maybe opened to the maximum position without danger of sudden variatiqns inthe water pressure. To provide a low pressure spray the unitary chambermust be of sufiicient size to accommodate a relatively large volume ofwater so that frictional resistance to flow is low. A relatively largevolume of water with respect to the out flow also promotes the settlingof any suspended matter. Still another advantage of the unitary chamberin place of a water jacketed mold is that the stream of water whichchills the mold can be seen by the operator and any stoppage or otherinterference with the stream can be easily detected.

A low pressure water supply can be provided in various ways but I havefound that a pressure reducing means such as a standpipe with suitableintake and outlet is a convenient means of maintaining a constant lowpressure supply of water to the spray chamber.

In using a low pressure water supply it has been found that asatisfactory chilling is obtained so long as that portion of theexternal surface of the mold shell corresponding to the internal surfacewhich is in contact with or close proximity to the molten and hotsolidified metal is flooded with water. By contact with or closeproximity to the mold shell by the molten and hot metal within the moldis meant both the region of the mold shell where there is an actualcontact and where the solidified metal has contracted slightly and lefta small space between it and the mold shell. Furthermore, there is aptto be less variation in pressure in a low pressure water supply thanwhere a high pressure supply is employed. This uniformity, in pressureis of course conducive to a uniformity in chilling. A low pressuresupply also tends to permit equalization of the temperature of the waterused, particularly where a reservoir is employed as an immediate sourceof water for chilling. The unitary; water chamber also permits a mixingof the water and tends to equalize any variation in temperature of theliquid. The uniformity of water pressure and temperature is ofparticular importance in the casting of light metal ingots whererelatively thin walled mold shells are used made of metal having arelatively high thermal conductivity, because variations in thechilling' condition on the exterior of the mold shell are quicklytransmitted to the metal within the mold.

The invention will be further described both as to method and apparatusin the following detailed description of the accompanying drawings, inwhich:

' Fig. 1 is a plan view of a preferred form of apparatus used inconnection with the casting of ingots;

Fig, 2 is a side elevation of the apparatus shown in Fig. 1;

, Fig. 3 is a cross sectional view taken on the line IIIIII of Fig. 1,together with certain additional casting equipment disclosed for thepurpose of clarity;

Fig. 4 is a broken and partial longitudinal sec- H0381 view of the spraychamber and inlet pipes; an

Fig. 5 is an enlarged broken cross sectional view of a spray chamber ofthe invention,

Referring to Figs. 1 and 2, frame III, which supports mold shells I6 andspray chambers 22 together with the necessary water supply pipes, ismounted on a support 62 and the entire assembly is pivoted on the memberI 2 so thatit can move through an are described by the dotted curvedline [4. In this manner the assembly can be moved into and out ofcasting position when desired.

The mold shells 5 are provided with lugs I8 having pins 20 therein whichregister with holes in the frame thereby maintaining the shells in afixed position. The mold shells preferably have relatively thin walls,say one-fourth inch in thickness, and are made of a metal having arelatively high thermal conductivity such as aluminum or copper or theiralloys. Surrounding each mold shell "5 is a. unitary spray chamber 22having end plates 24 bolted to flanges 26. As best shown in Fig. 5, thespray chamber has outer solid walls 34 and inner walls 32 provided withsuitably arranged spray holes through which water is directed at themold shell and ingot descending therefrom. Inside of the chambers and atboth ends thereof, perforated ballle plates 28 are located directly infront of water inlets 56, the baffle plates being held in place bysupports 30 attached to the top and bottom of the spray chamber.

A water supply of low pressure is provided from a standpipe 36 mountedon base 38. Water is adlet 44, swivel joint 48, and main line to branchpipes 52 and 54, where it enters the spray chambers through inlets 56,as shown by the arrowed dotted lines. For the purposeof draining thestandpipe, a pipe 58 and valve 60 are employed. The entrance of allwater to the system, it is noted. is controlled by the one valve 42. Thestandpipe may be of any convenient height so that the water pressure atthe spray may be on the order of from about 0.5 to 3 or 4 pounds persquare inch. The main water line from the standpipe must obviously be ofsuificient size to provide enough water to keep the spray chambersfilled and the sprays operating.

Figs. 4 and 5 present detailed views of a spray chamber. Water-supplypipes 50, 52. and 54 are shown in Fig. 4 with inlet pipe 56 threadedinto the end plate 24. Water entering through these inlets is preventedfrom directly striking the inner end walls of the spray chamber by theperforated bafiie plates 28. It will be noted that not all of the watercoming from the inlet necessarily passes through the bafiie plates. someof it passing over the top and under the bottom of the plates or aroundthe sides thereof. The water within the spray chamber is discharged insprays 92 against the mold shell and descending ingot through sprayholes 90 in the inner wall thereof. The spray chamber is preferablyspaced from the mold shell a distance of about 0.5 to 1 inch, themaximum distance in any event being determined by the distance which thewater spray can reach under the pressure employed. It is preferable thatthe inner wall of the spray chamber be parallel to the mold shell. Ithas been found that providing two banks of spray holes in the upperportion of the inner chamber wall and a ingle bank near the bottom givesan adequate supply of water to produce satisfactory light metal ingots.

It is preferable to position the holes as shown in Fig. 5 so that thespray strikes the mold and ingot in predetermined locations. However,such positioning i not essential to the use of a low pressure spray,except that the mold shell should be chilled above the level of themolten metal therein in order to avoid a fusion or burning of the shellby the hot metal inside of it. Generally, water should be sprayed on theemerging ingot as well as the mold shell, even though water sprayed onthe shell drains down upon the ingot surface. The location of the lowestspray is determined in part by the character of the metal or alloy beingcast; in some instances, the spray should strike the ingot a few inchesbelow the bottom edge of the mold, whereas in other cases the spraylocation is not critical. For the best results the lowest spray holesshould be located a sufficient distance above the bottom of the spraychamber to permit the settling of any sediment on the bottom withoutclogging the holes. It is known that where pipes have been employed toprovide a spray, the holes have become clogged with sediment and thisseriously interferes with obtaining a uniform chilling effect on themold shell and ingot. To remove any accumulated iii sediment in thebottom of the spray chamber it is only necessary to remove an end plateand scrape out the dirt, or pipe plug 85 may be removed if the sedimentcan be easily drained out. This ease of access to the spray chambergreatly facilitates maintaining the chamber in the best operatingcondition. One or two drilled holes 94 are located at the top of eachchamber to provide for the escape of air as the chamber is being filledwith water. The outer spray chamber wall 34 is preferably welded to theremainder of the chamher, as shown in Fig. 5. However, any other meansof attachment would be suitable providing a leak-proof joint isobtained.

The operating conditions under which the low pressure water spray isemployed are illustrated in Fig. 3. where the molten metal from anyconvenient source is delivered to a pouring trough I2. From this troughit passes through downspouts I4 to partially fill the mold shells andform a pool of metal 86 therein. The pool is maintained at substantiallythe same level during the casting operation. The flow of molten metal isconveniently controlled by raising and lowering the valve stem 18through the support mounted on bracket 82, which in turn rests upon thepouring trough. The molten metal is discharged from the downspoutthrough ports 16. Pool of metal freezes at the mold shell walls, and thethickness of frozen zone increases as the bottom edge of the mold shellis approached, however, the entire cross section of metal within theshell. may not be solidified at the level of said bottom edge of themold shell. The frozen zone is thick enough at this location underproper .chilling conditions to prevent any molten metal from leaking tothe surface. The ingot formed in this manner is lowered from the moldshell by the hydraulic elevator at a predetermined rate.

In addition to the foregoing features, Fig. 3 shows a cross section ofFig. 1 on line III-III. The frame It on which mold shells it aresupported can be seen. Pipe 50, 52, and 54 are shown as well as themanner of supporting pipe 54 from a T-member by welded construction.Flanges 26 at one end of the spray chambers with ibolt holes providedtherein are evident. The spray chambers having spray holes in the innerwall can also be seen. The ingots 88 rest on mold bottom 64 which inturn are mounted on platform 66. This platform is supported on plate 68against which bears the hydraulic ram arm III which raises or lowers theplatform. The hydraulic cylinder which operates the ram is located inthe casting pit which is not shown in the figures.

The water supply to the spray chambers is provided by filling thestandpipe to the desired height above the outlet 44 and maintaining thatlevel throughout the casting operation. Automatic means may, of course.be used to maintain any predetermined level of water such as a floatvalve. However, an overflow pipe placed :at the desired height, as shownin Fig. 2, provides a simple means of providing a constant pressure ifthe inflow of water is maintained in just a sumcient volume to cause aslight overflow.

Although one form of apparatus has been described, my invention is notlimited thereto but extends to other structures possessing the sameessential features which in operation produce the same result, namely,ingots having uniform internal structure which are relatively free fromsurface cracks and splitting. More particularly, the invention is notrestricted to the casting of rectangularly shaped ingots but isapplicable to other shapes and sizesv of ingots.

Water has been referred to hereinabove as the cooling medium employed.However, other fluid coolants can be used so long as the requisitechilling eilect is obtained.

I claim:

1. In the method of making ingots in open mold shells by a continuouscasting process wherein the mold shell is chilled by a water spray, thestep which comprises chilling said mold shell with a water spray under apressure of from about 0.5 to 4 pounds 'per square inch, said waterspray being directly delivered, in the form of a multiplicity of jets,from a relatively large body of water maintained adjacent the mold.

2. In the method of making light metal ingots in thin walled open moldshells by a continuous process .wherein the mold shell and emergingingot are chilled by a water spray, the step which comprises chillingsaid mold shell and ingot with a water spray under a pressure of fromabout 0.5 to 4 pounds per square inch, said water spray being directlydelivered, in the form of a multiplicity of jets, from a relativelylarge body of water maintained adjacent the mold.

. 3. In the art of making ingots by a continuous casting process in openmold shells, the method of minimizing splitting and surface cracking ofan ingot and improving the uniformity of its internal structurecomprising introducing molten metal into the mold shell, chilling theexterior of the mold shell andthe emerging ingot with a water sprayunder a pressure of from about 0.5 to 4 pounds per square inch, saidwater spray being directly delivered, in the form of a multiplicity 'ofjets, from a relatively large body of water maintained adjacent themold, said chilling being applied to at least that portion of theexternal surface of the mold shell corresponding to the portion of theinternal surface in contact with or in close proximity to the hot metalwithin the mold shell, and continuously withdrawing the ingot from saidmold shell.

' 4. In the art of making light metal ingots of relatively large crosssectional area by a continuous process in thin walled open shell moldsmade of a metal having a high thermal conductivity, the method ofminimizing splitting and surface cracking of an ingot and improving theuniformity of its internal structure comprising partially filling themold shell with molten metal and maintaining the pool of said moltenmetal at substantially the same level during the casting operation,chilling the exterior of the mold shell and emerging ingot with awaterspray under a pressure of from about 0.5 to 4 pounds per square inch,said water spray being directly delivered, in the form of a multiplicityof jets, from a relatively large body 0! water maintained adjacent themold, said chilling being applied to at least that portion of theexternal surface of the mold shell corresponding to the portion of theinternal surface in contact with or in close proximity to the hot metalwithin the mold shell, and continuously withdrawing the ingot from saidmold shell at the same rate at which freezing of the metal within themold shell progresses upwardly.

EDWIN ALFRED NICHOLLS.

